A photolithography technology to form circuit patterns in semiconductor devices plays an important role in advancement of the devices to have finer pitch and higher integration. A photomask used for forming such fine circuit patterns is formed with an electron beam writing technique. In the electron beam writing technique, an electron beam is applied to a mask blank to write a mask pattern, thereby forming a photomask.
For example, there is a multibeam writing apparatus using multiple beams. Compared to writing with a single electron beam, the multibeam writing apparatus can apply a lot of beams at a time, and hence improves throughput. The multibeam writing apparatus, for example, shapes an electron beam emitted from an electron gun into multiple beams through an aperture array having a plurality of holes and controls the multiple beams by blanking control to demagnify and deflect unshielded beams through an optical system, and then applies the demagnified and deflected beams to a mask blank.
The multibeam irradiation dose is controlled per beam depending on the irradiation time of each beam. Precise control of the multibeam irradiation dose requires high-speed multibeam blanking control (ON/OFF control). In order for that, the multibeam writing apparatus has a blanking aperture array mechanism having blankers arranged for respective multiple beams.
The blanking aperture array mechanism has control circuits for blanking control of respective beams and a circuit for transferring a control signal to each control circuit. The circuits become a heat source that generates heat in a writing process. In an electron beam writing apparatus, the blanking aperture array mechanism is used in vacuum. Therefore, the heat is hard to be released and may be accumulated in the blanking aperture array mechanism. In this case, there are problems of obstruction of proper blanking control due to the thermally-expanded mechanism, circuit malfunction, etc.